Hovercraft

[Conor Ryan]

I'm thinking that might work, just make sure your fan has the highest RPM you can give it. Watch your weight, that brings the end to a lot of homemade hovercrafts. Also what are your plans for steering the Hovercraft?

[sanddrag]

Wow, 11 hp. That is really big. I assume that is your propulsion engine? Do you have another engine for lift? Or are you going to somehow duct this one to give lift and propulsion?

[Tytus Gerrish]

okay here ya go this is how air should flow and lays out the concept

[Vince lau]

i was going to try this

http://amasci.com/amateur/hovercft.html

[adamrp]

Originally Posted by sanddrag

Wow, 11 hp. That is really big. I assume that is your propulsion engine? Do you have another engine for lift? Or are you going to somehow duct this one to give lift and propulsion?

Actually, the 11 HP is for lift. We have an 8HP engine for propulsion. I know, this is sort of backwards, but the 11HP has a vertical axle and the 8 has a horizonta axle, so we decided that rather than use differentials and belts we would do it this way. Off to work...

arp

[edomus]

[img]

[Mike Bortfeldt]

Edomus,

I recently built a 2-person hovercraft (Universal Hovercraft 12T4) from plans and can hopefully answer some of your questions. First, your 4'x8' platform should be able to lift one person as long as you can generate sufficient pressure from your lift fan (you don't mention what your fan blade was made out of or any of it's characteristics). Universal Hovercraft (UH) sells plans for a 3'x5' beginner hovercraft (UH-6F) that utilizes a 3 to 5 hp engine for both lift and thrust that can handle a 150 lb. payload so your engines are certainly large enough. You may want to think about buying these plans as they will have good general information on building a basic craft (skirt construction, operation, steering, etc.) that you can use when building yours. Larger engines are not necessarily a plus and can in some cases add weight for no useful purpose if your lift & thrust systems aren’t designed to utilize the engine’s capabilities. However, having existing engines available does negate a lot of the downsides.
One thing I would like to stress is to make sure you place guards around both your props. These blades will be going around 3000 RPM and could cause serious injury should they break or have some other failure. I say this from experience. After about 40 minutes of run time on the 12T4, I had a failure of the thrust system that resulted in a broken crankshaft on a 10 hp engine, and a prop split into two pieces. One of these pieces was thrown about 50' right through some lightweight steel mesh (luckily, no one was in the path.). Needless to say, there will be some changes when it’s repaired. You may want to think about making a real duct for the lift & thrust props as not only will you will get better performance, but it can also serve as guarding. You should wire in something like a lanyard kill switch to stop the engines in an emergency. Being homemade, safety should be a priority.
A few other thoughts based on your drawing and previous notes… 1) you may want to lower the hover height to about 6”, as with only a 4-foot width, it might be more stable. 2) I'm not sure if you really want a raised seat, as that will make your CG higher, again affecting stability. 3) I don't see any method to steer the craft. Typically 2 or 3 rudders are placed behind the thrust prop to direct the airflow and steer the craft.
Finally, make sure the props are designed to handle the stresses of running at the speed of the engines (possibly up to 3600 RPM). The props must also be well balanced. An unbalanced prop will cause significant forces and excessive vibration on the engine and craft as well as the prop itself.
Hope some of these comments help, and if you have any more questions, please ask and I will try to answer them. Just remember that the above comments are opinions only. My background is certainly not in hovercraft or prop design!

Mike